Self-Assembled hierarchical nanostructures as advanced SERS platforms

We investigated the creation of SERS-Active substrates by self-Assembling hierarchical structures of nanospheres (HSNs). The hierarchical architecture exploits the advantages of the well-known ordered configuration of hexagonally closed packed array (CPA) of nanospheres. An additional layer of upper nanospheres is utilized to generate dense and intense surface hotspots, strategically positioned at the nanogaps between adjacent nanospheres. A comprehensive numerical analysis was conducted, considering different ratios between the diameters of the bottom and upper nanospheres to optimize the SERS response. Two distinct self-Assembly fabrication techniques were explored to realize the designed HSNs, namely co-deposition and sequential deposition. Morphological analysis confirmed the successful formation of well-ordered hierarchical structures. We assessed the SERS performance of the fabricated samples utilizing biphenyl-4-thiol (BPT) monolayers as benchmark. The HSNs demonstrated superior SERS performance in comparison to single-layer CPA configurations.